The separation of solids and liquids is the basis of all wastewater treatment. Generally the separation involves a first mechanical step and then proceeds to a more aggressive phase separation prior to final treatment, i.e., after some type of mechanical separation, the next step in wastewater treatment is the recovery of the suspended solids or emulsion that exist in the particle range between settable solids and dissolved solids. A generally acceptable method for this separation is the use of a dissolved air floatation device. In this device, the liquid to be separated is treated with chemicals following which, fine bubbles in the range of 10 to 20 microns are introduced to the effluent stream. The effluent is then directed to an open tank where separation can occur. The float or suspended solid emulsion rises to the top of the tank and is swept off the top of the residual effluent with a mechanical rake or other collection means. The result is a clear or generally clear effluent and a concentrated emulsion.
Unfortunately, the method described above is not suitable for the separation of delicate or fragile emulsions where it is desired to cause the separation with something other than ambient air or where it is required to maintain anaerobic conditions of the emulsion. This is specifically applicable in the event that the emulsion is to be re-injected into an anaerobic digester for further use and processing.
There is therefore a need for a wastewater treatment method that is suitable for use with delicate or fragile emulsions, and is also compatible for use under anaerobic conditions.